This invention pertains to control valves and, more particularly, to a pilot-operated, 4-way valve having flow to either of two control ports and also a neutral position wherein flow through said control ports is blocked in order to provide a hold position for an operated device, such as a hydraulic cylinder.
The assignee of this application has, for many years, manufactured a 4-way valve having a pair of 3-way valve components and with positioning thereof under the control of a solenoid-operated pilot valve. This valve did not have the capability of holding pressure on a pair of control ports connected to opposite ends of a double-acting cylinder in a neutral position. Such capability could be provided by the addition of a pair of pilot-operated check valves. Pilot-operated check valves are well known in the art. However, operation thereof requires additional passages for directing pilot fluid thereto for causing operation. In the control valve disclosed in this application, pressure can be held in the control ports by the particular construction of the 3-way valve components of the control valve, along with the use of conventional check valves, without providing for pilot operation thereof.
A component of the control valve disclosed herein is a pressure-reducing valve for establishing a relatively low pilot pressure and after pilot operation permitting full flow through the valve components with the pressure-reducing valve having a closed, balanced position. The assignee of this application developed a pressure-reducing valve with this capability several years ago, but such valve was not associated with the components of the control valve as disclosed herein to produce the operative device disclosed in this application.
For several years, there has been a solenoid-controlled, pilot-operated, 4-way valve on the market with a pair of control ports having their connection to a supply passage and to a reservoir controlled by two pairs of oppositely-acting check valves, with a pair of pilot pistons operable to open a passage between one control port and the reservoir and, at the same time, positively engage a valve element to close off flow from the supply passage to the same control port. This control valve additionally had a valve section for establishing a relatively low pilot pressure for pilot action followed by closing of the valve section to permit full line pressure delivery to a control port. This solenoid-controlled, pilot-operated, 4-way valve is constructed whereby pilot pressure acting on a pilot piston is in direct opposition to the line pressure delivered to a control port for operation of a cylinder whereby a relatively large valve for handling large volume and high pressures involves substantial forces in maintaining control positions. Additionally, the valve section for setting the pilot pressure is not balanced when closed and in opening must act against substantial resisting forces.